在Entity Framework或LINQ中进行选择时，如何将日期列分组为较不精确的格式？

Question

I am collecting data within every ten seconds ( six records in a minute ). Using Entity Framework or LINQ , I want to obtain the average of the records within a every minute.
Simply, Date column is in ( %Y.%m.%d %H:%i:%s ) format, and i want to group by ( %Y.%m.%d %H:%i ) format in mysql using Entity Framework or LINQ

Answer 1

Assuming that you mean you have a date time column you can group by the DateTime properties Year , Month , Day , Hour , and Minute .

var results = from row in db.SomeTable
              group by new 
              { 
                  row.Date.Year, 
                  row.Date.Month, 
                  row.Date.Day, 
                  row.Date.Hour, 
                  row.Date.Minute 
              } into grp
              select new 
              { 
                  YMDHM = grp.Key
                  SomeAverage = grp.Average(x => x.SomeValueToAverage)
              };

Then when you iterate the results you can turn the values in YMDHM back into a DateTime . Here's an example where you could turn the results into a Dictionary .

var dictionaryOfAverages = results.ToDictionary(
    x => new DateTime(x.YMDHM.Year, 
                      x.YMDHM.Month,  
                      x.YMDHM.Day,  
                      x.YMDHM.Hour,  
                      x.YMDHM.Minute,  
                      0), 
    x => x.SomeAverage);

On the other hand if you actually mean you are storing the date time in the DB as a formatted string then the following would be what you want

var results = from row in db.SomeTable
              group by new row.Date.SubString(0, 16) into grp
              select new 
              { 
                  YMDHM = grp.Key
                  SomeAverage = grp.Average(x => x.SomeValueToAverage)
              };

This is assuming that your string formatted dates look like "2013.05.08 07:25:33" If the format isn't fixed width with leading zeros for month, day, and/or hour you'd have to do something like row.Date.SubString(0, row.Date.Length - 3) instead